This invention relates to an apparatus and process for separating and washing a concentrate of solids from a solids-containing fluid. More particularly, this invention relates to a concentrator-washer and process for dynamically separating a filtrate and a concentrate of solids from a solids-containing fluid and washing impurities from the concentrate in a continuous process within one apparatus.
Various types of filtration devices have heretofore been known for concentrating the solids content of a fluid. For example, U.S. Pat. No. 3,437,208 describes a device wherein a solids-containing fluid is pumped under pressure across the filtering surfaces of assembled hollow filter members so that a portion of the fluid is passed through the filtering surfaces and into the supporting filter member structures. The fluid is thereafter removed as a filtrate, and solids tending to remain on the filtering surfaces during the filtering operation are continuously returned into the solids-containing fluid to increase the concentration of solids within the filtration device and thereby form a thickened slurry for subsequent removal from the device. U.S. Pat. No. 3,437,208 also describes a series of filtering and washing steps utilizing the vessels of three separate filtration devices interconnected by conduits. Each of the filtration devices has a hollow shaft. The hollow shaft of the first filtration device carries off filtrate from the first vessel, and the second vessel is provided with a hollow shaft for discharging wash liquid as waste. Wash liquid from the third vessel, removed through the hollow shaft of the third vessel, is added to the second vessel and thus removed as waste through the hollow shaft of the second vessel. Fresh wash liquid is added to an inlet in a conduit between the second and third vessels which carries the slurry output of the second vessel. U.S. Pat. No. 3,437,208 indicates that for the described apparatus to be housed in a common vessel partitions must be provided in the vessel as well as a hollow shaft with independent channels for carrying off the filtrate and the wash liquid.
In U.S. Pat. No. 1,264,635 a filter and wash system is described in which six separate filter units are used. Three of the filter units separate sludge from filtrate and three are used as washers to wash the sludge. The three washer units are arranged in series with the first washer unit receiving all the sludge from the three filter units A, A.sup.1, and A.sup.2. Wash liquid in washer unit 1 is supplied by the liquid from washer unit 2. The wash liquid removed in washer unit 1 is then added to the unfiltered material passed through the filter units A, A.sup.1, and A.sup.2. The sludge in turn removed from washer unit 1 together with the wash liquid from washer unit 3 is then added to washer unit 2. The sludge from washer unit 2, together with fresh wash water is then added to washer unit 3 from which the sludge is removed while the the wash liquid is recycled to be added to the sludge coming from washer unit 1 and going into washer unit 2.
In contrast to the teachings of U.S. Pat. Nos. 3,437,208 and 1,264,635, the apparatus of the present invention is a unitary device which is contained within one housing which avoids the necessity and expense of a hollow shaft having independent channels for carrying off filtrate and wash liquid as in U.S. Pat. No. 3,437,208. Further, the device of this invention in contrast to the '208 patent does not require partitions between the separating and washing chambers but instead has dynamic means in the form of rotating discs between the filter elements. Further, in contrast to U.S. Pat. No. 1,264,635 in which the concentrate is formed as a precipitate on the bottom of the device after being squeezed out of the input material between two counter-rotating filter discs, the concentrate generated in and by the apparatus and process of this invention is continuously formed as the filtrate is removed from the solids-containing fluid as it is advanced through the concentrating and washing chambers of the apparatus.
Means have also heretofore been known for cleaning an accumulation of solids material which has deposited on the surfaces of filtering diaphragms in filtration devices. In some instances, such filtration devices have been periodically dismantled to remove the filtering diaphragms for cleaning purposes. In other instances, a backwash arrangement has been used to wash the solids deposited on the filtering surfaces, for example, by means of water forced into and through the interior of a hollow filter and through the filtering diaphragms. In still other instances, such as is described in U.S. Pat. No. 1,000,540, a filter cake has been produced in a centrifugal device by the centrifugal separation of the solids from the filtrate. Subsequent to the formation of the filter cake it is washed by adding wash water to the interior of the centrifuge through the same valve and piping as the centrifuge material. After the filter cake has been washed the machine is disassembled and the cleaned filter cake is removed from the machine. Each of these washing processes is a discontinuous process which requires a shutting down and dismantling of the apparatus.
Other examples of discontinuous processes are found in U.S. Pat. Nos. 1,920,126 and 3,108,951. Thus, in U.S. Pat. No. 1,920,126 solid material such as wax contained in wax-bearing mineral oil is separated in a filter press and washed with a solvent which is added within the interior of the filter press after the formation of the filter cake. The solvent addition is continued until the cake is completely washed. The press is then opened and the cake removed. In U.S. Pat. No. 3,108,951 a filter cake in a centrifugal device is washed after formation of the cake within the centrifuge by the addition of wash water which is then centrifugally passed through the cake to wash the cake.
Apparatus is also known for refining oil, such as shown in U.S. Pat. No. 956,065 in which liquids containing oil are forced through a plurality of screens which break up the liquid and separate the impurities therefrom. In that apparatus provision is also made for adding gas, air or other fluid material to carry out the purifying process for the liquid. Also, a method is described in U.S. Pat. No. 3,346,418 for washing impurities from clay-like and jelly-like materials by continuous addition and removal of a liquid medium which is a solvent for the impurities, the removal occurring upon passage of the particle-carrying liquid through a porous tube.
Other processes are known for separating or extracting soluble impurities from a solid by counter-flowing a solvent through the solid material. These processes shown, for example, in U.S. Pat. Nos. 2,547,577, 2,686,192, 2,998,307, 3,111,393 and 3,275,472 operate by adding a fresh solvent to the solids at the last stage of the extraction process, collecting that solvent and progressively adding, collecting, and introducing the contaminated solvent to the preceding stages of the process. This method of adding solvent operates to extract soluble material by counter-flowing the solvent through the material as it progresses through the device.
Thus, while many varied processes and devices have been proposed for either separating a solid, washing a solid, or extracting soluble material from a solid, no process or apparatus has heretofore been known for preparing a washed concentrate from a solids-containing fluid by a continuous process in which the solids-containing fluid has the solids separated, concentrated and washed on a steady basis in a dynamic concentrator-washer within and incorporating a unitary housing as taught according to the present invention.